1. Field of the Invention
The present invention relates to a link mechanism having two links coupled by a joint.
2. Description of the Related Art
Hitherto, there has been known a link mechanism of a robot or the like, in which a first link and a second link are connected by a joint and the second link is pivoted with respect to the first link by the driving force of an electric actuator disposed at a joint section (refer to, for example, Patent Document 1).    Patent Document 1: Japanese Patent Application Laid-Open No. 2016-74055
According to the link mechanism described in Patent Document 1, the driving force of the joint for causing the second link to pivot with respect to the first link is determined by the driving force of the electric actuator. More specifically, a torque sensor is disposed at the joint section, and the driving force of the electric actuator is controlled by a controller on the basis of a detection value detected by the torque sensor.
Meanwhile, in a link mechanism of a robot, the stiffness of the second link with respect to the first link is preferably changeable. When the pivoting movement of the second link with respect to the first link is stopped, the second link is desired to remain stationary with respect to the first link even if an external force is applied to the second link or the second link is desired to pivot with respect to the first link if an external force of the same magnitude is applied, depending on external circumstances.
However, according to the configuration described in Patent Document 1, the driving force of the electric actuator is merely transmitted to the joint (a strain inducing member) through a speed reducer from the rotating shaft of the electric actuator, thus making it difficult to change the force for maintaining the pivot of the second link with respect to the first link (the stiffness of the joint) according to external circumstances. Further, to change the stiffness of the joint, a transmission actuator is required to be actuated after receiving a signal of the torque sensor of the joint, so that an action will be inconveniently delayed in response to external circumstances.